UE terminals, such as cellular phones, can operate both indoors and outdoors. When the UE terminals are outdoors, the base station uses beam forming functions through smart antennas to enhance communication performance and reliability with the UE terminals. For example, signal-to-noise ratio (SNR) may be increased by using smart antennas.
FIG. 10 illustrates a conventional system 1000 that is used outdoors. The system 1000 includes a base station 1010 with antennas 1015 producing multiple beam lobes 1020. Beam forming circuitry 1012 coupled to the antennas 1015 controls the formation of the beam lobes 1020. Each beam lobe 1020 represents a wireless communication channel—a radio resource—used by the base station 1010 to communicate with a UE terminal. The radio resource may be either a common channel or a dedicated channel. When the base station broadcasts a same message to multiple UE terminals simultaneously, the common channel is used. But in most instances, the base station communicates with the UE terminals individually through dedicated channels.
In FIG. 10, four separate beam lobes 1020 are shown, each of which can represent individual dedicated channel, i.e. each beam lobe is a separate radio resource to communicate individually with four separate UE terminals. Each radio resource is separately identifiable based for example on a time slot (for TDMA systems), frequency (for FDMA systems), or spreading code (for CDMA systems).
Each beam lobe 1020 has a preferred direction, and any UE terminal within the range of the beam lobes 1020 may communicate with the base station 1010. The directional nature of the beam lobes 1020 enhances the quality of communication between the base station and the UE terminals by increasing the communication range of the base station, as compared to a similarly powered omni-directional signal. Also, the signal quality is enhanced by reducing the interference of the signals since the amount of overlap between the beam lobes is minimized.
Each beam lobe's directionality is achieved by controlling the amount of transmission power to each antenna 1015 for the radio resource associated with the beam lobe. For a particular radio resource corresponding to a particular beam lobe 1020, the amount of power of the wireless signal emanating from each antenna 1015 for that particular resource is also controlled by the beam forming circuitry 1012.
The beam forming circuitry 1012 sets a transmission weight factor (or simply weight factor) for each antenna for the particular radio resource. The weight factor can range anywhere between 0 and 1 representing between no power to full power being emanated from the antenna for the particular resource. The number of weight factors can be finite. For example, if the number of weight factors is nine, the weight factors may take on individual values 0.0, 0.125, 0.250, 0.375, 0.5, 0.625, 0.75, 0.875, and 1.0. The direction of each beam lobe 1020 can be controlled with finer detail as the granularity—i.e. the number—of the weight factor values between 0 and 1 increases.
For conventional systems, the number of weight factors is large. For a typical coverage of a communication sector of the base station ranging from −60 degrees to +60 degrees with a 1 degree accuracy, a total of 121 sets of weight factors are needed, where each set corresponds to a certain beam pointing direction within the −60 degrees to +60 degrees angular interval. The size of each set is determined by the number of antenna elements—where eight antenna elements is a typical number—and each individual weight factor can be any number between 0 and 1, with e.g. a four-decimal digit representation such as 0.1479. In the typical case, a total of 8×121 four-digit weight factors would be required. In this way, multiple beam lobes 1020, each representing a different radio resource, are produced simultaneously as seen in FIG. 10.
The system 1000 illustrated in FIG. 10 works well outdoors. Although the same system can be used to communicate with UE terminals located inside a building, it does not work as well indoors. Within the building, the UE terminals will all generally be in a same direction from the base station since they are all located close to each other. When dedicated channels, i.e., separate radio resources, are used for communication between the base station and each of the UE terminals located in the building, the beam lobes corresponding to the radio resources will also be formed in the same general direction. This increases the likelihood of interference. Also, no radio resource can be simultaneously reused by the base station to communicate with another UE terminal. Still further, signal bouncing and multiple access interference (MAI) is a bigger issue indoors due to the presence of physical features such as walls, floors and ceilings. MAI is caused by multiple user equipments using the same frequency allocation at the same time.
There are dedicated indoor solutions available. One indoor solution consists of placing small (also known as micro or pico) base stations in many places in a building. There are both upgrade and operational drawbacks to this solution. For upgrades, the main drawbacks includes complexity and the significant time needed to perform upgrades to hardware and software since each installation site must be visited. During operation, unnecessary interference is generated within the building since no centralized radio resource allocation can be provided. As a result, spectral efficiency of the communication network is severely compromised. Furthermore, handover procedure between adjacent base stations is difficult or non-existent.
Another indoor solution is to install a long RF feeder cable in the building connected to a base station located in the building and to connect several antennas to this RF feeder cable via a RF combining device placed at separate locations in the building. With this solution, it is not possible to use a specific antenna for transmission/reception. Instead, all antennas radiate power and hence generate unnecessary interference at the locations where a UE terminal may not be located.
These and other indoor solutions are dedicated to indoors and are separate from the existing outdoor based systems. Dedicated indoor solutions are expensive since they require separate equipments and increase complexity since they must be interfaced with the existing outdoor systems. Increased complexity is usually accompanied by decreased reliability.